Galvanic cells may generate large quantities of gas under certain conditions during use. Since these cells are required to be tightly sealed at all times in order to prevent loss of electrolyte by evaporation or leakage, high internal gas pressures may develop. Such pressures may cause leakage, bulging or possible explosion of the cell if not properly vented. If a vent valve is employed, it generally is resealable in order to avoid drying out of the electrolyte over the life of the cell and to prevent ingress of oxygen from the atmosphere which can cause wasteful corrosion of the anode.
In the past, several different types of resealable pressure relief vent valves have been used for releasing high internal gas pressures from inside a sealed galvanic cell. One type of valve that has been commonly used consists basically of a valve member such as a flat rubber gasket which is biased into sealing position over a vent orifice by means of a resilient member such as a helical spring. The resilient member or spring is designed to yield at a certain predetermined internal gas pressure so as to momentarily break the seal and allow the gas to escape through the vent orifice.
Another type of resealable pressure relief vent valve that has been tried is that disclosed and claimed in U.S. Pat. No. 3,293,081 issued to J. L. S. Daley on Dec. 20, 1966. This resealable vent valve basically includes an annular seal gasket, such as an O-ring, which is maintained in sealing position around the periphery of the vent orifice by means of an arc shaped resilient member or spring. The resilient member or spring is designed to yield and permit radial movement of the seal gasket so as to momentarily break the seal and allow the passage of gas through the vent orifice when a predetermined high internal gas pressure is reached inside the cell.
Another type of resealable vent is disclosed in U.S. Pat. No. 3,415,690 to Richman issued on Dec. 10, 1968. In this vent, a flat elastomeric seal gasket overlies the vent opening and is retained in place by a resilient terminal cap on the top of the cell. This vent operates in basically the same manner as the vents previously described.
In U.S. Pat. No. 3,664,878 to Amthor issued on May 23, 1972, a resealable vent is disclosed which comprises a resilient deformable ball of elastomeric material positioned to overlie a vent orifice provided within the cell's container. A retainer means is positioned over the resilient ball for maintaining the ball in place over the vent orifice and in contact with a valve seat provided around the peripheral edge portions of the vent orifice and for compressing and deforming the resilient ball into a flattened configuration forming a normally fluid-tight seal between the flattened ball and the valve seat. The resilient ball is capable of undergoing further temporary deformation upon the buildup of a predetermined high internal gas pressure inside the container so as to momentarily break the seal and allow gas to escape through the vent orifice.
A major problem encountered with resealable pressure relief vent valves of the types just described is that they are bulky and/or difficult to incorporate into the cell assembly. Furthermore, these pressure relief vent valves are expensive to manufacture and most are not adaptable for incorporation into miniature size cells. In addition, some of the prior art resealable vents as exemplified by the foregoing patents are not suitable for low pressure venting.
An inexpensive low pressure resealable vent closure is disclosed in U.S. Pat. No. 4,020,241 to Henry Heinz, Jr. Specifically, a galvanic cell is disclosed having a resealable vent closure consisting of a resilient elastomeric sponge gasket disposed and compressed between the cover of the cell and the upper wall of the cell's container and designed to vent low pressure gas buildup along the cover-gasket interface and/or container-gasket interface.
An inexpensive high pressure vent closure is disclosed in U.S. application Ser. No. 782,401 filed in the name of T. R. Potts et al. on Mar. 29, 1977. Specifically, a galvanic cell is disclosed having a conventional radial seal and wherein at least one gas venting passage is disposed at the interface of the top surface of the cover and the curled over rim of the cell's container, said passage being defined as a recess in the cover disposed below the curled over rim and/or a notch in a portion of the curled over rim.
As discussed above, resealable, high pressure relief vent valves are generally bulky and/or difficult to incorporate into a cell assembly while low pressure vent means for some cell systems may not adequately and sufficiently prevent loss of electrolyte through leakage or prevent ingress of oxygen from the atmosphere which could cause wasteful corrosion of the anode.
It is, therefore, an important object of this invention to provide a primary high pressure seal in conjunction with a secondary resealable vent valve for use in a galvanic dry cell.
Another object of this invention is to provide a resealable venting means operable upon release of a primary high pressure seal for safely venting high pressure gases from within a cell.
Still another object of this invention is to provide a resealable vent valve as a backup seal for a primary high pressure seal vent for galvanic dry cells which requires a minimum number of parts and which is, therefore, easy to assemble and inexpensive to manufacture.
Another object of this invention is to provide a resilient elastomeric sponge gasket as the active member of a secondary vent seal.
Another object of this invention is to provide a resealable vent as a backup for a primary high pressure vent for galvanic cells and which is adaptable to various diameters of drawn or extruded cylindrical cell containers.
The foregoing and additional objects will become more fully apparent from the following description and the accompanying drawings.